WASHINGTON — The United States is doing little to defend the planet against potentially devastating asteroids, and is not doing the basic searches that Congress has ordered, according to a report released yesterday.

While most of the really big and obvious threats are being found, almost nothing is being done to find the smaller objects that are arguably a more likely threat, the strongly worded report from the National Academy of Sciences said.

“It means we are not looking for the small ones which can cause huge damage on earth,” astronomer Mike A’Hearne, of the University of Maryland, who helped chair the committee that wrote the report, said in a telephone interview.

“Why has nothing been done? I don’t know,” added A’Hearne.

He said it was not clear whether the administration of President Obama, who has declared his support for science but is struggling with an economic downturn and budget deficits, would work any harder to do more.